ShortPixel’s image optimization offers 3 levels of quality.
- Lossy offers the best compression rate and is the best option for most users. The images processed with the Lossy algorithms are the smallest optimized images you can get. So, if the speed of your site is paramount and you want the best balance between optimization and picture quality, we recommend you continue using Lossy optimization.
- Glossy is the best choice if you still care about GTmetrix, PageSpeed Insights, or some other page speed tester, but you believe that a slight loss of page speed is an acceptable compromise for top-notch image quality. This is the best option for photographers and other professionals that use very high-quality images on their sites and want the best compression while keeping the quality almost the same.
- Lossless images are pixel-by-pixel identical with the originals, but they offer a smaller size reduction compared to either Lossy or Glossy processed files. In some rare cases, you will need to use this type of compression. Some technical drawings or images from vector graphics are possible situations, or if you simply want your images to remain untouched.
Feel free to run some tests here.